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Milk may protect against bowel cancer

Drinking milk may protect against bowel cancer, suggests a new study on the dairy-eating habits of more than half a million people.

Colon cancer is now the third most common cancer in the world. Almost a million people are diagnosed with the disease each year.

Research has long hinted at a connection between calcium and reduced colorectal cancer risk. Animal studies showed that calcium, an important signalling ion for colon cell organisation, can slow cell growth in the intestinal lining and limit early stage tumour development. A previous study showed that diarrhoea-causing infections also seem impede the cancer’s progress possibly because they trigger a massive influx of calcium to gut cells.

But epidemiological research has yet to conclusively link eating calcium-rich foods with a decreased colon cancer risk – probably because most studies have been small and lack the statistical power to detect the moderate effects of dietary calcium.

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So Eunyoung Cho at Brigham and Women’s Hospital and Harvard Medical School, US and colleagues pooled the raw survey data from 10 different studies, extracting information on daily intake of milk, cheese, yoghurt and calcium supplements as well long-term diagnoses of colorectal cancer. Almost 5000 people from the study groups were diagnosed with the disease during follow-up periods.

Cheese and yoghurt

They found that people who drank at least one 250 millilitre glass of milk a day were 15 per cent less likely to get colorectal cancer than people who drank almost none. Cheese and yoghurt had only weak effects, probably because people ate much less of them.

Overall calcium consumption, which included supplements, was also associated with decreased risk to a point. After about 1000 milligrammes of daily calcium – around three large glasses of milk – the benefits levelled off. High levels of calcium have also recently been linked to prostate cancer.

“Because calcium is involved in so many functions in body, we need to understand the full range of health effects before making recommendations,” Cho told New Scientist.

But while the trend appeared strong, Emad El-Omar, a gastroenterologist at the University of Aberdeen, UK, still believes the key to preventing colon cancer is lifestyle.

“It’s a very complex situation, but the bottom line is if you eat fat and don’t exercise, you’re at risk for developing colon cancer,” he says. “How you link calcium into that is difficult.”